1. Field of the Invention
The present invention relates to an arrangement for establishing multi-address and conference call connections in a switching system comprising line terminators which are respectively associated with the incoming and outgoing lines, and more particularly to such operations in a switching system which comprises a connection memory common to all line terminators and in which there is associated with each line terminator one storage cell which, for the duration of a connection, contains the allocation between a specified calling line terminator and a specified called line terminator, and comprising devices for scanning the line terminators and for addressing the connection memory, whereby, through the evaluation of the address contained in the addressed storage cell of the connection memory, the line terminators are interconnected, in each case, only for the purpose of transmitting a message character.
2. Description of the Prior Art
In Telex switching systems, in addition to establishing a connection between subscribers, there is also the additional demand for the possibility of establishing a connection between more than two subscribers. This is then referred to as a multi-address connection or a conference call connection. The term "multi-address connection" is intended to denote that a plurality of subscribers are each capable of receiving messages transmitted from a specified subscriber, while the term "conference call connection" is intended to denote that the subscribers participating in the connection are not only capable of receiving, but also of transmitting messages. In order to set up multi-address and conference call connections, the call numbers of the subscribers participating in a multi-address connection are first transmitted from the subscriber station, which desires to set up such a connection, to the switching station, and these call numbers are evaluated at the switching station for the purpose of establishing a connection to the individual called subscriber.
In known switching systems, so-called multi-address circuits or conference call circuits, respectively, are provided for this purpose in the switching system, which receive the data transmitted by the calling subscriber station, which establishes connections to the called subscribers, and connect the latter. The messages transmitted by a calling subscriber station then reach all other subscribers participating in the multi-address connection.
In more recent switching systems, in which the connection established is carried out pursuant to the control of a central program, such installations are no longer provided. Switching systems of this type contain a subscriber terminator for each incoming and outgoing line, and a common connection memory for all subscriber terminators in which a separate storage cell is associated with each subscriber terminator. Those particular data which are required for the transmission of messages between interconnection subscribers are respectively entered in the storage cell for the duration of a connection. The entry of the data in the connection memory takes place, in each instance, at the beginning of a connection, from a central location, e.g., due to programmed operating cycles, in a central processing unit. A storage cell contains, among other things, the number of that particular line terminator with which the line circuit, to which the storage cell is allocated, is connected. All line terminators are constantly scanned in a cyclical fashion, whereby the storage cell in the connection memory associated with the scanned line terminator is also simultaneously addressed. If a message character has arrived on an incoming line and if, at the time of scanning, the line terminator associated with this line has the message character available at its output, the address contained in the addressed storage cell is read out therefrom. This address is the line number of that particular line terminator to which the message character must be transferred. By virtue of the address, the respective line terminator is activated, the message character is transferred to the latter and transmitted to the called subscriber by way of the outgoing line. Subsequent to the transmission of the message character to the addressed line terminator, scanning of the additional line terminators is resumed. In this manner, all line terminators are scanned, and message characters occurring to the addresses contained in the connection memory are transmitted to specified subscriber terminators. A switching system such as this is described, by way of example, in the publication "Siemens System EDX," Edition 1, January 1975.